Field of the Invention
The present invention relates to a data processing apparatus and a print data generating method, and in particular, to a technique for making an offset in an arrangement of a plurality of dot arrangement patterns used to binarize image data.
Description of the Related Art
In a dot arrange pattern, “printing (dots present)” or “non-printing (no dots)” is determined in each pixel of a unit of one pixel×two pixels which has a double resolution of 1,200 dpi in a longitudinal direction, according to a gradation value of image data. In binary data generation, gradation values indicated by image data of 600 dpi can be converted into binary data (dots present/no dots) within the range of one pixel×two pixels, using dot arrangement patterns corresponding to the gradation value indicated by the image data. This binarization technique enables data processing, transfer, and the like to be executed in a low-resolution data form, preventing the data processing and transfer from needing a very long time. A memory capacity needed for a printing apparatus may be reduced.
Japanese Patent Laid-Open No. 2014-031001 describes a configuration that uses, as a unit, a matrix in which a plurality of dot arrangement patterns corresponding to one gradation value indicated by image data is arranged in an X direction and a Y direction and repeatedly uses and applies the matrix to the image data for binarization, so that texture in the print image is reduced. Specifically, each time the matrix is repeatedly used, an offset process is executed in which the an offset value is differentiated with respect to the arrangement of codes in a code table that determine the arrangement of the dot arrangement pattern, thus changing the arrangement of the plurality of dot arrangement patterns in the matrix. This enables a reduction in regular texture in the print image when the matrix for one gradation value is repeatedly used for the pixel area.
The size, in each of the X and Y directions, of the matrix or the code table, which is the above-described unit repeatedly used, is typically represented as the power of 2 such as 4, 8, or 16. In this case, when, for example, the size in the X direction is 4 and each of the pixel numbers of 0 to 3 for making offset is selected at an equal probability, this is suitable for eliminating the above-described regular texture.
In contrast, the size, in each of the X and Y directions, of the matrix or the code table for the dot arrangement pattern may not be the power of 2. However, in determination of the offset value, for example, if the number represented by data bits that generate a random number is the power of 2, the offset value may be indivisible by the size of the code table. In this case, the frequencies of generation of a plurality of offset values corresponding to the code table may not be even. As a result, the frequencies at which the offset pixel numbers are selected are biased, possibly resulting in another texture problem with the print image.